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ME Super
10-23-2012, 03:46 PM
IIRC a ferricyanide bleach is a rehalogenating bleach. This would turn your developed paper negative back into an unexposed piece of paper, which after exposure to room light would quickly turn solid black. The dichromate and permanganate bleaches remove the developed silver, leaving the remaining silver halides behind. The reexposure to light gets you a developable positive image.

holmburgers
10-26-2012, 04:49 PM
A friend had a different approach to this and we tried it out last night. It really using the basis of a lith article by Ed Buffaloe in blinking eye. http://unblinkingeye.com/Articles/NbyR/nbyr.html
A sheet of paper (MG RC)was exposed in camera for twice the metered exposure (in testing it was found to get the best end result), then under a enlarger set to about 700mm high and lens stopped down to f22 we preflashed the paper for 6-8 sec. Developed , Stop, lights on, Bleach, Wash, Clear, redeveloped in same developer, wash, we then fixed and washed again get to clear the slimy feel. End result is pretty good. That's the basics anyway, we need to do some more testing using some originals which have been exposed the same to determine what different preflash times do to the contrast.

Thanks for sharing the details; I need to try this someday.

andy_k
10-27-2012, 07:44 PM
andy, this sounds like a really fascinating method. A unique & intriguing approach!

Are you utilizing an exposure at a certain point in the development, or is it some kind of pre/post-exposure flash?

It's remarkable to me that such a good positive can be got by simply exploiting exposure at the right time... whoa!

it seems that about halfway to developing out the image (30-40 seconds) if i just hit the bathroom lights for a split second (halogen, not bad), or hit it with a high power xenon strobe (much better).

i really have had very inconsistent results so far. unfortunately i burnt the bulb on the higher watt strobe unit i was using (24W bulb), and trying to get the paper to reverse with a vastly smaller bulb is not working at all. i haven't put any time into more exposures with the bathroom light, although that's what i was working with at first.

i think this process has a lot of potential for producing some very very interesting pictures, as unique and unreproducible direct images.

andy_k
10-29-2012, 05:56 PM
okay, took some time this morning to revisit the process!

here's my setup in my bathroom:
i've obviously got my camera, homemade softbox (on a really wimpy Pentax AF160 i got for free, supported by a rubik's cube on top of the focusing screen), single halogen light source, 1:8(ish?) ilford multigrade developer, a water bath for stopping and washing, and rapid fix.

the whole approach is very imprecise, because i'm dealing with expired paper and didn't want to get my phone to use as a timer while i was in there banging the portraits out. i metered the bathroom light at EV 3.5 for EI 12 (which i estimated a full stop slower for the paper, roughly--so more like a true EV 1.75 for EI 6) with my handy little incident meter, and the softbox i'm eyeballing off the exposure chart on the back as a half-stop under normal ( EI 25 @ f8, 1m = EI 6 @ f2.8, <1m + power reduction from diffuser). the flash exposure came out fairly close to true, though a little under. however the mostly-flash exposure (shortest shutter-open time) came out the nicest.

the procedure for each was to expose, fog the plate a touch with light through the crack at the bottom of the door (~1 s), develop to completion in darkness (~1 min), flash the bathroom light to initiate reversal (0.3 - 0.1s, you get a good look at the negative at this point), develop to completion (~50 s), put in water stop bath for ~10s letting the developer work its way out (and at this point your eyes have well adjusted again and can clearly see your plate has darkened), fix for whatever feels comfortable and wash in the sink for a couple minutes.

these are the fruits of my efforts today, arranged top to bottom, right to left. the first was a gross underexposure (i had accidentally left the stop at f8). the second shot was as lit as i could possibly get it for ~4s exposure and the flash, and reversed with ~0.25s of bathroom light--it came out with badly blown highlights on my nose and forehead that did not reverse. i believe that this unwillingness of fully developed halides to reverse means there are very hard limits on the maximum contrast ratio that can be captured with this process.

the rest of the shots in the right column were experimenting with exposure and flash time. when i do proper scans of these images i'll make a post of my recollected exposure data (whatever that'll mean) in a later post.

the two (i feel) more successful exposures on the left column were the last two, and were a bit different. these exposures were for shorter times, roughly 1.5s, and when flashed with the overhead light showed almost no density at all as a negative image. in fact, for the top image on the left the paper was completely white, i couldn't see any density at all when i flashed it, and agitated it for a good minute and a half in the developer hoping i could get something out of it. the lower image was about the same for exposure and density when i initiated the reversal, and just trusted that i'd see something. obviously they're much lighter in tone, but i'm happier with them as there are very little to no unreversed highlights. i believe this is a factor of both shorter exposure times to avoid blowing highlights on the front end, and more gentle reversing exposures.

andy_k
10-30-2012, 11:06 PM
here're some scans of the photographs I made yesterday, all calibrated to maximize the scanner's range and replicate the relative tonal characteristics of each image. i scanned in color because there are slight hue differences with different exposure levels. i have not manipulated these images at all to make them comparable, but the actual photos have a characteristic gray-brown hue to them, rather than the blue or green color these scans show.

first, a little more technical information about the procedure. i placed myself in the focal plane, which i established with a no. 2 diopter and racking the bellows in all the way at wide open (Sekor 80mm f 2.8 blue dot). camera is loaded with lightly flashed paper, lights on, expose, lights off, develop to completion (1 min), flash for reversal, develop to completion (+water bath soak to a stop), fix, lights on and figure out what to do for the next one. as above, i metered the bathroom light at EV 3.5 for EI 12 and eye-balled exposure from there.

the first image was an overall failure. the following (second) plate was made with a 5s exposure with the flash. reversal exposure was roughly 0.2s. obviously blown highlights on my nose and forehead retained their density in the reversal process, and average density was high with a low contrast.
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this next plate was exposed for about 3.5s with the flash and the door open (with light from my room lights and outside through the window). the reversing flash was a touch longer, about 0.25s. nice high density on the frame edge, and shadows, less held-over black blown out highlights, although the overall contrast is ridiculous and detail is only on my ear and neck where the exposure was lower.
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this plate had an exposure of 3s with the door closed, and the flash. the reversing exposure was about 0.25s. better detail, no blown highlights, but again low contrast and higher average density.
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this plate had an exposure of 6s, without the flash (didn't fire the first time so did a double exposure). reversing exposure was much shorter, about 0.1s. terrible blowing of highlights again. however, i was encouraged by the very high overall contrast generated by the short reversing exposure.
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this plate was essentially all bulb, ~1.5s exposure. reversing exposure was at first 0.1s, but i saw the negative showed no perceptible density after a full minute of development. after a few seconds of development in the dark and not seeing any color change i flashed again for 0.1s, and developed for a full minute and let it rest in the water bath hoping something would come out. great tonal range, detail, lower average density, better overall contrast. this is my favourite photo, basically an accident (but a happy one).
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this plate was ~2s exposure with flash, and a 0.1s reversing exposure (maybe shorter). i trusted that the nearly-zero observed negative density would produce a positive image, and produced a high contrast, low maximum density image. there is a black mark in my left eye (remember, rotated inverse images) from a blown unreversed highlight. as a side note, i'd ripped the corner off to test my developer that had been sitting in the tray at the start of the day to see if it was good having been mixed a couple days before (it wasn't, so i started this series of photos with fresh).
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this was my most successful image from my first experiements with this approach, and was produced essentially by accident. scanned with the same scanner, same settings, for comparison. exposure for this image was with my flash (bare) held at arm's length, shot twice, ~20s exposure in lower incident light only through my bedroom window. reversing exposure roughly 0.2 seconds (i'm guessing, this was a month ago).
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so it seems to me that there is a LOT of leeway for producing a recognizable photograph, but definitely needs dialing in to get good repeatable results. flatter, even lighting seems to have the ability to produce good detail and appealing contrast. from my experiments it seems that the strength of the latent image is less important than the duration of the reversing exposure--longer secondary exposure can compound with long initial exposures and solarize the crap out of your image. good, healthy developer seems to help the process along to generate good positive density, but definitely hurts tonality with fogged highlights and lower contrast.

this information is all but useless, and is really just a place to start for anyone else interested in experimenting. i'm sure you'll all pay closer attention to what you're doing than i have. :)

andy_k
11-02-2012, 12:53 PM
i cut more paper just yesteryday, now trying it with some highly expired Kodak Multigrade II RC. it seems much slower than the Ilfospeed 3 my previous images were made with.

also, i (actually!) measured my developer concentration, and played with the process there. my estimations on concentration were way off, a triple strength dilution (1:3 rather than 1:9 as per bottle instructions for Ilford Multigrade) is required for the image reversal to occur. strong-but-close-to-normal concentrations resulted only in an off-color fog when the secondary exposure was applied.

i'll post more results soon.

erikg
11-02-2012, 03:15 PM
I tried this out some time ago, mostly just to see if I could make it work. I exposed the paper to a negative in the enlarger, and then reversed it, so I had a negative to negative process. It's pretty cool to do, and it would be a good pairing with a pinhole camera. I never could get fiber based paper to work without some staining. I guess that seems rather obvious but until you try it you never know for sure.

SMBooth
11-02-2012, 04:30 PM
I never could get fiber based paper to work without some staining. I guess that seems rather obvious but until you try it you never know for sure.

Not to me, Why?

I was going to try FB paper.

andy_k
11-03-2012, 10:15 AM
yeah i doubt the emulsion support has a huge effect on how it will respond to the process, but i've found huge differences in behavior between the Ilfospeed and Multigrade II. definitely different papers are going to respond very differently, not to mention developer combinations.

anyone have a good idea for how to make a rudimentary 6x6 step tablet? i'd really like to begin taking this process halfway seriously.

holmburgers
11-03-2012, 11:59 AM
Andy, does your 6x6 camera have a darkslide per chance (like on a Hasselblad film back for instance)? If so, you could pull it out in increments, giving a -5 exposure on a white/gray ground each time you pull it out. If you can pull it out 11 times in the length of 6cm, dividing the film into 11 sections, the first exposed portion will eventually get +5 exposure and the intermediate sections will get +4, +3, +2, +1, 0, -1, -2, -3, -4, -5.

You could do the same thing under an enlarger, but it'd just be a bit trickier.

andy_k
11-03-2012, 03:36 PM
man, i totally wish it did. great idea.

no the C330's are the RB67's of the TLR world, chunky, featured, and awesome. no darkslide though. however when i'm next in the darkroom i'll try that out, with a better meter on the reversing exposure that way too.

erikg
11-04-2012, 06:28 AM
Not to me, Why?

I was going to try FB paper.

It does work on FB, but there was some staining that I couldn't solve. When you look at what the paper is going through it isn't surprising, at least to me. Don't let that stop you from trying, that was just my experience.

andy_k
12-06-2012, 06:39 AM
I went to the darkroom this afternoon and put some time into getting a better idea of what's going on with the reversal process, and how to try and optimize the results. For this round of tests I essentially tried to replicate the conditions that have worked in the past for me in my bathroom, and intend to further experiment in a controllable fashion rather than just guessing and checking.

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This is what I came up with today. Developer was Ilford Multigrade at 1:3 dilution. Paper was some old Kodak Multigrade RC II. I set up the enlarger without filters, using a 50mm f2.8 projection lens (for speed and the size of the projected circle). The picture above shows all the stuff I exposed, first a test for max black, then the smaller strips on which I tried a nine stop exposure range. The larger strips were a dialed-in five stop exposure range in 1/3 stop increments.

For this test I began quantifying my exposure in lux-seconds to have a universal unit of comparison for the different exposure intensities between the much slower and smaller intensities which create the negative image, and the short intense exposure which induces the tone reversal.

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A close-up of my results, and the development information for the big strips. As you can see, the process is sensitive to changes in pre-flash development and flash duration/intensity. My feeling is that a slightly lower developer concentration might provide better overall contrast range compared to the results I achieved today. Also, I'm curious about what, if any, effect a shorter and brighter (but same lux-second) reversing flash would have.

I can post my complete exposure data if anyone is interested, but it will likely be quite different for other paper/developer combinations. My estimations of about 0.2s flashes for the self-portraits I posted earlier in the thread seemed to produce the best results today (I calibrated the enlarger to match the measured brightness of the light at counter-top distance). Maximum black on the test strip, both negative and reversed, was achieved at ~32 ls exposure, minimum reversed density (2 stops less than max negative black) at ~ 10ls, and max reversed density (starting 1.67 stops than min rev density) at 3.2 ls and less. The reversing exposure was 64 ls for the nominal 0.2s exposure at a measured 7 EV, twice the amount of light to produce max black.

Thoughts? Comments? Criticisms?

edit: looking carefully, as I hadn't yet today--I struggled to get these tests finished with a migraine coming on, which I've only now come clear of--test strips 4 and 7 have a reasonably large difference in development and exposure times, producing very comparable and good results. As with my earlier feeling, this procedure does have a fairly wide sweet spot.

andy_k
12-07-2012, 04:54 AM
Alright, another go 'round, looking to see the effect of changing developer concentration in conjunction with variations in exposure.
The exposure range for these strips was from 2.5 ls to 12.5 ls (the 10 ls zone still the lightest after reversal) in 1/6th stop increments. Reversing exposure the same, other than where indicated. The first six strips were developed at 1:4 dilution, with the seventh at 1:5.
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it appears to me that developer concentration has a similar effect to shifting exposure/development when push or pull processing on film; there is an inherent compromise between tonal range and tonal contrast.
it seems that at these very high developer energies/concentrations that the relatively small variations in exposure have a smaller overall effect, and need to be within a narrower range, than developer concentration.

Any input? I'd love to know what Photo Engineer might say about any of this, or anyone with more technical knowledge than i have.

andy_k
12-12-2012, 03:21 AM
Hey again gents (and ladies?),

Quick feedback from my experience using powerful flash heads to stimulate the reversal process: it makes a huge difference. Without really having numbers to relate to the above information, or surviving visual (scannable) results to give you, I noticed a massive increase in overal tonal range and contrast using studio strobes to hit the negative image with.

The reason I don't have anything to show you to prove it is a result of my recycling of fairly old fixer in my portable paper-picture kit. Having long since dissolved even the aluminium off of the bottle seal, and smelling strongly of ammonia, the fixer somehow bleached the developed positive images from very nice looking black and white to a creme and rusty brown. No idea what was going on there, but sadly the great reversal results were lost.

Anyone else try out my approach yet? Particularly with a larger format camera?

NedL
12-12-2012, 10:26 AM
I haven't tried it but I've been reading with interest these past weeks and hope you keep relating your experience! Neat idea to try to get this process under control.

andy_k
12-18-2012, 01:58 AM
It appears that a functional EI of 25 produces really great latent images that are very suitable for reversal, provided that your scene is illuminated with only 2 - 4 stops of luminance range. Reversing with a very powerful strobe is unquestionably the superior method, compared to bright halogen light.

I suggest giving it a try if you're interested, see what happens.

andy_k
01-08-2013, 08:36 PM
I'm sorry, but I don't see how a more powerful re-exposure can INCREASE the effective ei...
UNLESS you are overexposing in the 2nd exposure to the point that you're gettin solarization/partial reversal or total reversal happening...that may be the case and if it's controllable, then this may be worthwhile...

yeah, not sure if you saw my earlier posts but this is exactly it. the second exposure that i'm doing is not a fogging exposure in a chemical reversing process, but a solarizing exposure that i'm trying to control. the higher EI rating for the paper is just something that i'm estimating based on my test results as a more suitable latent image for my solarized direct reversal process (it's all done in one development, the paper never leaves the soup).

andy_k
01-08-2013, 08:47 PM
i'm now quite done catching up on badly overdue darkroom projects, but as time permits me in the coming months i'll be attempting some ultra large format macro reversal images. i'll update here in the thread as progress is made.

NedL
01-08-2013, 11:02 PM
I'm looking forward to reading them... I find this fascinating and hope to play with it myself eventually.